Quality RTOS & Embedded Software About  Contact  Support  FAQ  Download  Menu      Quick Start Supported MCUs PDF Books Trace Tools Ecosystem Home FreeRTOS Books and Manuals FreeRTOS About FreeRTOS What is an RTOS/FreeRTOS? A Compelling Free Solution A Better Type of Open Source Coding Standard/MISRA/Testing Features Overview Licensing Site Map Features / Getting Started... Quick Start Guide Tasks & Co-routines More About Tasks... Task States Task Priorities Implementing a Task Idle Task and Idle Hook Queues, Mutexes, Semaphores... Queues Binary Semaphores Counting Semaphores Mutexes Recursive Mutexes Direct To Task Notifications Introduction ...As Binary Semaphore ...As Counting Semaphore ...As Event Group ...As Mailbox Stream & Message Buffers ...ISR to Task Streams ...Core to Core Messages Software Timers Introduction Timer Service Daemon Task Timer Daemon Configuration One-Shot Vs Auto-Reload Resetting a Timer Event Groups (or 'flags') More About Co-routines... Co-routine Status Co-routine Priorities Implementing a Co-routine Scheduling Co-routines Limitations and Restrictions Quick Co-routine Example Standard Demo Examples Source Code Organisation More Advanced... Creating a New Project FreeRTOSConfig.h Trace Features Low Power Support Run Time Stats Blocking on Multiple Objects Deferred Interrupt Handling Static Vs Dynamic Memory Memory Management Memory Protection Support Stack Overflow Protection Hook Functions Thread Local Storage Pointers How FreeRTOS Works Introduction Fundamentals Multitasking Basics Schedulinig Basics Context Switching Real Time Applications Real Time Scheduling Implementation Building Blocks Development Tools The RTOS Tick GCC Signal Attribute GCC Naked Attribute FreeRTOS Tick Code AVR Context Saving the Context Restoring the Context Detailed Example Putting It All Together Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7 RAM Constrained Design Tips Page 1 Page 2 Page 3 Page 4 Page 5 Porting Guide Windows Simulator Posix/Linux Simulator Legacy Trace Facility Demo Projects Standard Demos Basic Demos Hardware Independent Modifying a Demo TCP/IP Demos Supported Devices & Demos Official & Contributed Definitions Simple List of Ports Officially Supported Demos TCP/IP Demos API Reference PDF Reference Manual Task Creation TaskHandle_t (type) xTaskCreate() xTaskCreateStatic() vTaskDelete() Task Control vTaskDelay() vTaskDelayUntil() uxTaskPriorityGet() vTaskPrioritySet() vTaskSuspend() vTaskResume() xTaskResumeFromISR() xTaskAbortDelay() Task Utilities uxTaskGetSystemState() vTaskGetInfo() xTaskGetApplicationTaskTag() xTaskGetCurrentTaskHandle() xTaskGetHandle() xTaskGetIdleTaskHandle() uxTaskGetStackHighWaterMark() eTaskGetState() pcTaskGetName() xTaskGetTickCount() xTaskGetTickCountFromISR() xTaskGetSchedulerState() uxTaskGetNumberOfTasks() vTaskList() vTaskStartTrace() ulTaskEndTrace() vTaskGetRunTimeStats() vTaskSetApplicationTaskTag() xTaskCallApplicationTaskHook() 'SetThreadLocalStoragePointer() 'GetThreadLocalStoragePointer() vTaskSetTimeOutState() xTaskGetCheckForTimeOut() RTOS Kernel Control taskYIELD() taskENTER_CRITICAL() taskEXIT_CRITICAL() taskENTER_CRITICAL_FROM_ISR() taskEXIT_CRITICAL_FROM_ISR() taskDISABLE_INTERRUPTS() taskENABLE_INTERRUPTS() vTaskStartScheduler() vTaskEndScheduler() vTaskSuspendAll() xTaskResumeAll() vTaskStepTick() Direct To Task Notifications xTaskNotifyGive() vTaskNotifyGiveFromISR() ulTaskNotifyTake() xTaskNotify() xTaskNotifyAndQuery() xTaskNotifyAndQueryFromISR() xTaskNotifyFromISR() xTaskNotifyWait() xTaskNotifyStateClear() Queues xQueueCreate() xQueueCreateStatic() vQueueDelete() xQueueSend() xQueueSendFromISR() xQueueSendToBack() xQueueSendToBackFromISR() xQueueSendToFront() xQueueSendToFrontFromISR() xQueueReceive() xQueueReceiveFromISR() uxQueueMessagesWaiting() uxQueueMessagesWaitingFromISR() uxQueueSpacesAvailable() xQueueReset() xQueueOverwrite() xQueueOverwriteFromISR() xQueuePeek() xQueuePeekFromISR() vQueueAddToRegistry() vQueueUnregisterQueue() pcQueueGetName() xQueueIsQueueFullFromISR() xQueueIsQueueEmptyFromISR() Queue Sets xQueueCreateSet() xQueueAddToSet() xQueueRemoveFromSet() xQueueSelectFromSet() xQueueSelectFromSetFromISR() Stream Buffers xStreamBufferCreate() xStreamBufferCreateStatic() xStreamBufferSend() xStreamBufferSendFromISR() xStreamBufferReceive() xStreamBufferReceiveFromISR() vStreamBufferDelete() xStreamBufferBytesAvailable() xStreamBufferSpacesAvailable() xStreamBufferSetTriggerLevel() xStreamBufferReset() xStreamBufferIsEmpty() xStreamBufferIsFull() Message Buffers xMessageBufferCreate() xMessageBufferCreateStatic() xMessageBufferSend() xMessageBufferSendFromISR() xMessageBufferReceive() xMessageBufferReceiveFromISR() vMessageBufferDelete() xMessageBufferSpacesAvailable() xMessageBufferReset() xMessageBufferIsEmpty() xMessageBufferIsFull() Semaphore / Mutexes xSemaphoreCreateBinary() xSemaphoreCreateBinaryStatic() vSemaphoreCreateBinary() xSemaphoreCreateCounting() xSemaphoreCreateCountingStatic() xSemaphoreCreateMutex() xSemaphoreCreateMutexStatic() xSem'CreateRecursiveMutex() xSem'CreateRecursiveMutexStatic() vSemaphoreDelete() xSemaphoreGetMutexHolder() uxSemaphoreGetCount() xSemaphoreTake() xSemaphoreTakeFromISR() xSemaphoreTakeRecursive() xSemaphoreGive() xSemaphoreGiveRecursive() xSemaphoreGiveFromISR() Software Timers xTimerCreate() xTimerCreateStatic() xTimerIsTimerActive() xTimerStart() xTimerStop() xTimerChangePeriod() xTimerDelete() xTimerReset() xTimerStartFromISR() xTimerStopFromISR() xTimerChangePeriodFromISR() xTimerResetFromISR() pvTimerGetTimerID() vTimerSetReloadMode() vTimerSetTimerID() xTimerGetTimerDaemonTaskHandle() xTimerPendFunctionCall() xTimerPendFunctionCallFromISR() pcTimerGetName() xTimerGetPeriod() xTimerGetExpiryTime() Event Groups (or 'flags') xEventGroupCreate() xEventGroupCreateStatic() vEventGroupDelete() xEventGroupWaitBits() xEventGroupSetBits() xEventGroupSetBitsFromISR() xEventGroupClearBits() xEventGroupClearBitsFromISR() xEventGroupGetBits() xEventGroupGetBitsFromISR() xEventGroupSync() FreeRTOS-MPU Specific xTaskCreateRestricted() vTaskAllocateMPURegions() 'SWITCH_TO_USER_MODE() Co-routines CoRoutineHandle_t (type) xCoRoutineCreate() crDELAY() crQUEUE_SEND() crQUEUE_RECEIVE() crQUEUE_SEND_FROM_ISR() crQUEUE_RECEIVE_FROM_ISR() vCoRoutineSchedule() Contact & Support Contact Free Support Forum Commercial Support FAQ FreeRTOS Interactive! Contributed Vs Official Code Contributing Source Code Upload / Download Contributions Quick Start Guide Support Forum ⇓ Download Source ⇓ FreeRTOS+ Ecosystem  FreeRTOS+ TCP:  Thread safe TCP/IP stack  SafeRTOS:  TUV certified RTOS  OpenRTOS:  Commercial Licensed RTOS  Fail Safe File System:  Ensures data integrity  FreeRTOS BSPs:  3rd party driver packages  Trace & Visualisation:  Tracealyzer for FreeRTOS  CLI:  Command line interface  WolfSSL SSL / TLS:  Networking security protocols  RTOS Training:  Delivered online or on-site  IO:  read(), write(), ioctl() interface FreeRTOS+ Lab Projects  IoT MQTT:  PubSub messaging protocol  IoT HTTPS  Request + response msging  IoT Task Pool:  A shared collection of tasks  FreeRTOS+POSIX:  POSIX threading API  FreeRTOS+FAT:  Thread aware file system Hint: Use the tree menu to navigate groups of related pages   uxSemaphoreGetCount [Semaphores] semphr. h UBaseType_t uxSemaphoreGetCount( SemaphoreHandle_t xSemaphore ); Returns the count of a semaphore. Parameters: xSemaphore   The handle of the semaphore being queried. Returns: If the semaphore is a counting semaphore then the semaphores current count value is returned. If the semaphore is a binary semaphore then 1 is returned if the semaphore is available, and 0 is returned if the semaphore is not available. [ Back to the top ]   [ About FreeRTOS ]   [ Privacy ]   [ Sitemap ]   [Report an error on this page] Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News FreeRTOS v10.2.1 is available for immediate download. MIT licensed, includes 64-bit RISC-V, NXP Cortex-M33 demo & Nuvoton Cortex-M23 demo & STM32H745 dual core (AMP) demo. New Updates to MIT licensed IoT MQTT and POSIX libraries are now available. New library IoT HTTPS is available.  Includes demo projects. View a recording of the “OTA Update Security and Reliability” webinar, presented by TI and AWS. Careers FreeRTOS and other embedded software careers at AWS. FreeRTOS Partners